Process for compensating for the incorrect operation of measuring devices caused by external influences

ABSTRACT

A process for compensating for an incorrect operation of measuring devices fitted with a programming section caused by external influences. The measuring devices and a sensor responding to the influence are fitted in a chamber exposed to the influencing factor. When the influencing factor changes, measurements from the measuring device and the sensor are detected by a data processing system which provides the programming section of the measuring devices with signals compensating for the incorrect operation caused by the influencing factor. To perform such a process rapidly and thus economically, the influencing factor is continuously changed and the current output value of the sensor and the current measurement provided by the measuring device are detected with a timing predetermined by the data processing system.

FIELD OF THE INVENTION

The present invention relates to a process for compensating forincorrect operation of measuring devices caused by changes intemperature.

BACKGROUND INFORMATION

Many known measuring devices do not perform as they should under anexternal influence. In particular, measuring devices do not performcorrectly when temperature is the external influence. This occursbecause many measuring devices, or the actual measuring section of suchmeasuring devices, supply output values that are no longer in thenecessary proportion to a measured quantity on the input side when thetemperature changes. For example, semiconductor-based pressure sensorsused in the form of pressure or differential-pressure transducers inmeasuring devices are frequently so highly dependent on temperature thatthey no longer satisfy the required measuring accuracy. The specifiedmeasuring accuracy can be achieved only by compensating for thetemperature-caused errors. Such compensation can be carried outespecially well in measuring devices having a programming section. Thiscan be done because, in combination with a data processing system, theprogramming section can be used to set the relevant measuring device sothat its output value remains almost unaffected by changes intemperature. In the case of pressure or differential-pressuretransducers, these devices are known as intelligent sensors. Theintelligent sensors include the sensor and an associated programmingsection.

A process is described in a publication "Piezoresistive und kapazitiveDrucksensoren mit integrierter Signalvorverarbeitung" (Piezoresistiveand Capacitive Pressure Sensors with Integrated Signal Preprocessing),joint project 1989 to 1992, Final Report Technische Universitat Berlin,Fraunhofer-Institut fur Mikroelektronische Schaltungen und Systeme,Duisberg, and University of Stuttgart, Vol. 9, 1994, pp. 19-20. In thisconventional process, pressure sensors having thermal characteristicswhich are to be compensated for are placed in a temperature test cabinetwhich is heated in stages for the purpose of compensation. Each time thecabinet is heated to the next higher temperature, implementation of theconventional compensation process is delayed for a certain period oftime to ensure that the pressure sensors to be compensated for haveindeed reached the temperature set in each case in the cabinet. Oncethis temperature has been reached, a measurand is supplied from thepressure sensor to a data processing system via a multiplexer. Once therelevant temperature values and the output values of the pressuresensors have been entered in this manner in the data processing systemat the predetermined temperature levels, the data processing systemgenerates signals compensating for the temperature dependence andprovides them to the programming section of the pressure sensors,thereby ensuring that the output values provided by the pressure sensorsare proportional to the measured quantities on the input side regardlessof the changes in temperature.

The conventional process for compensating for the incorrect operation ofmeasuring devices (fitted with a programming section) caused by changesin temperature is very time-consuming because detection of the measurandmust be delayed for a relatively long period each time the temperatureis increased in the chamber of the temperature testing cabinet until themeasurement devices to be tested have reached the temperature of thechamber. This considerably increases the production time for themeasuring devices or pressure sensors, which makes the manufacture ofpressure sensor relatively expensive.

U.S. Pat. No. 5,319,965 describes a pressure recording device in whichpressure measurement results unaffected by changes in temperature areobtained by taking into account calibration values stored in a memory.However, this patent does not describe how these calibration values areobtained.

Moreover, a method in which a range of temperatures is traversed withoutstopping to automatically detect the dependence of measured quantitieson temperature is described in German Patent Application No. 33 40 207.Measuring signals corresponding to the measured quantity dependent ontemperature are detected with a temperature sensor at predeterminedtemperatures. An error function that is available for the temperaturecompensation of measuring signals obtained individually is formed fromcorresponding value pairs, and another temperature sensor is required tocarry out the actual temperature compensation.

A differential-pressure transducer in which a temperature sensor isintegrated into the transducer is also described in "IECON '84",Proceedings of 1984 International Conference on Industrial Electronics,Control and Instrumentation, Tokyo, Japan, Vol. 2, Oct. 22-26, 1984, pp.1081-86. The temperature sensor is used to obtain and take into accountcorrecting quantities to account for the temperature dependence of theoutput value of the differential-pressure sensor belonging to thistransducer. The publication does not describe a specific way in whichthis is accomplished.

A method for detecting and recording the performance of a pressuresensor depending on changes in temperature is also described in U.S.Pat. No. 4,845,649. This patent does not describe the specifics of howthis is accomplished.

European Patent Application No. 0 580 462 describes a process that islargely identical to the process explained in detail above.

SUMMARY OF THE INVENTION

The present invention provides a process for compensating for incorrectoperation of measuring devices fitted with a programming section causedby changes in temperature. The measuring devices with the programmingsections are placed in a chamber that is exposed the changes intemperature. The chamber also contains a temperature sensor. Themeasuring devices with the programming section, as well as thetemperature sensor, are connected to a data processing system. Ameasurand quantity is applied to the measuring devices and thetemperature in the chamber is changed. The measurands are determinedeach time the temperature is changed are measured and processed by thedata processing system. Signals compensating for the incorrect operationcaused by the changes in temperature are provided to the programmingsection of the measuring devices by the data processing system.

An object of the present invention is to provide a process forcompensating for incorrect operation of a measuring device fitted with aprogramming section caused by temperature so that the process can becarried out much more quickly and therefore more economically.

To achieve the object, measuring devices, each with a temperature sensorpositioned immediately adjacent to the actual measuring section, areoperated in the process, the temperature is changed continuously and theoutput value of the temperature sensor and the measurand provided by themeasuring devices are detected with a timing predetermined by the dataprocessing system.

An important advantage of the process according to the present inventionis that it can be carried out much more quickly than the conventionalprocess described above, thus considerably reducing the productioncosts. Since the temperature is changed continuously in the processaccording to the present invention, i.e. there is no delay until themeasuring device reaches the temperature in the chamber when usingtemperature as the influencing factor, this eliminates the waiting timesneeded in the conventional process. If greater temperature differencesoccur between the temperature in the chamber containing the measuringdevices and the temperature of the measuring device itself, this doesnot cause any problems because these (highly uniform) temperaturedifferences can be easily compensated for mathematically using the dataprocessing system, since these differences are present in the form ofempirical values or can be determined by experiment. This also ensuresthat, if the pressure sensor has a pressure and differential-pressuretransducer, the actual measuring section of the measuring device willhave largely the same temperature as the adjacent temperature sensor sothat temperature differences between the pressure sensors and thetemperature sensors will produce only slight measurand deviations thatare largely independent of temperature and can be corrected later on bycalibrating the pressure characteristic.

It is particularly advantageous if, in the process according to thepresent invention, the temperature is continuously increased from aninitial low value, the compensating signals are generated when thetemperature reaches a maximum value and are transmitted to theprogramming section of the measuring devices. The temperature is thencontinuously decreased from its maximum value to the low value whilemeasuring the output value of the sensor and the measurand with thetiming predetermined by the data processing system. Then, the measurandsare evaluated in the data processing system to check the compensationresult. This exemplary embodiment utilizes the fact that the heatedchamber must be cooled down after the compensation process before themeasuring devices are removed; the cooling process is then used to checkthe compensation result.

In an advantageous exemplary embodiment of the process according to thepresent invention, a sensor detecting static pressure (pressure sensor)is assigned to the transducer to compensate for the influence of staticpressure on the performance of a differential-pressure transducer usedas the measuring device. This allows to set a differential-pressuretransducer relatively quickly so that its output value remains largelyunaffected by the static pressure.

The present invention can also be used to advantage when a singleprecision pressure sensor responding to the influence of pressure isplaced in the chamber to linearize the pressure characteristic ofmeasuring devices in the form of pressure or differential-pressuresensors, and the pressure in the chamber is changed continuously; theoutput value of the precision pressure sensor and the values of thepressure or differential-pressure transducers are measured with a timingpredetermined by the data processing system during the change inpressure.

In the process for linearizing the pressure characteristic, it isadvantageous if the pressure is continuously increased from an initiallow value to a maximum value and, once the pressure in the chamber hasreached the maximum value, signals linearizing the characteristic aregenerated by the data processing system and transmitted to theprogramming section. The pressure is then continuously decreased fromthe maximum value to the low value while measuring the output value ofthe precision pressure sensor and the measurands with the timingpredetermined by the data processing system, and the measurands areevaluated in the data processing system to check the linearizationresult. An advantage of this exemplary embodiment of the processaccording to the present invention is that the measurands for checkingthe linearization result can be obtained and evaluated simultaneouslywhen the pressure is released in the chamber containing the measuringdevices.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows an exemplary embodiment of an arrangement for carryingout the process according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The FIGURE shows an arrangement including a furnace 1 whose innerchamber 2 holds several measuring devices 3, the thermal characteristicof which is to be compensated for here. The FIGURE shows only onemeasuring device 3, and additional devices of the same construction areindicated by dots.

Each measuring device 3 includes an actual measuring section 4 and aprogramming section 5. Actual measuring section 4 can be a pressuresensor if measuring device 3 is a pressure or differential-pressuretransducer. Programming section 5 is permanently assigned herepreferably to a semiconductor-based pressure sensor 4, i.e. anintelligent sensor. A temperature sensor 6 is positioned immediatelyadjacent to pressure sensor 4 so that this temperature sensor 6 alwayshas the same temperature as adjacent pressure sensor 4. Temperaturesensor 6 is also connected to the programming section.

The measuring device 3 is connected to a multiplexer 8 via a firstelectrical connection 7 to supply measurands from measuring section 4and temperature sensor 6 via a bus system 9 to a data processing system10, which is most suitably designed as a personal computer. Signals aretransmitted from data processing system 10 to programming section 5 overanother electrical connection 11 between multiplexer 8 and actualmeasuring section 4. These are signals compensating for the thermalcharacteristic and generated in the manner described below.

Several additional measuring devices with assigned temperature sensors,which are indicated by dots in the FIGURE, are connected to dataprocessing system 10 in the same manner as temperature sensor 6 viaadditionally suggested electrical connections and via multiplexer 8.

As shown in the FIGURE, furnace 1 is provided with a heating controlelement 13 which is controlled by data processing system 10 so that thetemperature in chamber 2 of furnace 1 changes continuously from a lowvalue to a maximum value. The low value and the maximum value aredefined by the temperature range in which the measuring devices to becompensated for are to operate without suffering the effect of thetemperature.

As described above, a pressure or differential-pressure transducer isused in the exemplary embodiment as measuring device 3, which is why apressure calibration device 14 is connected to furnace 1. Using thispressure calibration device, a certain pressure can be set in furnace 1from data processing system 10, and the pressure then forms the measuredquantity on input side for all measuring devices or transducers 3.

According to the present invention, the process is carried out so that,when pressure or differential-pressure transducers are used as measuringdevices 3 to be compensated for, chamber 2 in furnace 1 is first cooleddown to -40° C. Starting at this lower temperature, data processingsystem 10 causes the temperature in chamber 2 to increase continuouslyvia heating control element 13. As the temperature in chamber 2increases continuously in this manner, a measurand provided by sensor 4is picked up using multiplexer 8 via connection 7 with the timingpredetermined by data processing system 10. The output value oftemperature sensor 6 is detected at the same time, assigned to theappropriate measurand of pressure sensor 4, and stored in dataprocessing system 10. Measurands provided by pressure sensor 4 andoutput values of temperature sensor 6 are recorded continuously in thismanner until a maximum temperature value of approximately +85° C. isreached; the same procedure is carried out for the remaining pressuresensors using multiplexer 8. Once the maximum temperature of +85° C. hasbeen reached, the measured values are evaluated by data processingsystem 10 and appropriate signals compensating for the thermalcharacteristic are generated. These signals are transmitted toprogramming sections 5 of pressure sensors 4 and used to compensate forthe thermal characteristic of the respective transducer.

After programming section 5 has processed the signals from dataprocessing system 10, the temperature in chamber 2 of furnace 1 is againreduced continuously, the output value of pressure sensor 4 is againmeasured via connection 7 with the operational timing of data processingsystem 10, and the output value of temperature sensor 6 is alsodetermined via connection 12. These values are again processed in dataprocessing system 10 and the compensation result is checked to see if itis satisfactory. The same procedure is carried out simultaneously forthe remaining pressure sensors using multiplexer 8.

When carrying out the process according to the present invention forcompensating for the external influence of static pressure in adifferential-pressure transducer with a programming section as themeasuring device, a difference in pressure with a steady rise in staticpressure is applied to the transducer, together with what are normallyseveral identical transducers. To detect the static pressure, eachdifferential-pressure transducer is equipped with a pressure sensor,which is connected to the programming section in the same manner as thetemperature sensors in the exemplary embodiment described above. A dataprocessing system, which is connected to the programming section of therespective transducer and is programmed accordingly, supplies thesignals compensating for the influence of the static pressure to theprogramming section.

If, when using pressure or differential-pressure transducers as themeasuring devices, linearization of the pressure characteristic is to becarried out as part of the process according to the present invention, apressure calibration device controlled by a data processing system isused to continuously increase the pressure. The measurands provided bythe pressure sensors of the transducer are detected largelysimultaneously by the data processing system via a multiplexer. Signalslinearizing the pressure sensor characteristic are generated from thesemeasurands in the data processing system and transmitted to theprogramming unit. When the pressure is released, the characteristic ischecked as the pressure decreases continuously. A measurand deviation,which may result from the time difference between pressure selection andmeasurand detection is corrected later on by calibrating the minimum andmaximum values.

What is claimed is:
 1. A process for compensating for an incorrectoperation of a measuring device caused by temperature changes in themeasuring device, the measuring device including a programming section,the process comprising the steps of:(a) providing the measuring devicein a chamber, the measuring device including an actual measuringsection, the measuring device providing at least one measurand value;(b) providing a temperature sensor in the chamber immediately adjacentto the actual measuring section, the temperature sensor providing atleast one output value; (c) coupling the programming section and the atleast one temperature sensor to a data processing system, the dataprocessing system processing the at least one measurand value; (d)providing a measured quantity to the measuring device; (e) after step(d), gradually and continuously changing a temperature in the chamber ata constant rate of rise; (f) while performing step (e), detecting the atleast one output value and the at least one measurand value, thedetecting step being performed at a predetermined frequency, thepredetermined frequency being predetermined by the data processingsystem; and (g) providing, by the data processing system, at least onecompensating signal to the programming section, the at least onecompensating signal compensating for the incorrect operation of themeasuring device as a function of the at least one output value.
 2. Theprocess according to claim 1, further comprising the stepsof:continuously increasing the temperature from an initial low value;when the temperature reaches a maximum value, providing the at least onecompensating signal to the programming section; continuously decreasingthe temperature from the maximum value to the low value while detectingthe at least one output value and the at least one measurand value atthe predetermined frequency; and evaluating by the data processingsystem the at least one measurand value to determine a compensationresult.
 3. The process according to claim 1, wherein the measuringdevice is one of a pressure transducer and a differential-pressuretransducer, and the actual measuring section is a first pressure sensor.4. The process according to claim 3, further comprising the stepof:assigning a second pressure sensor to the measuring device tocompensate for an influence of a static pressure on the measuringdevice.
 5. The process according to claim 3, further comprising the stepof:providing a single precision pressure sensor in the chamber tolinearize a pressure characteristic of the measuring device, the singleprecision pressure sensor measuring a pressure in the chamber andproviding at least one output pressure value; continuously changing thepressure; and detecting the at least one output pressure value and theat least one measurand value with the predetermined timing as thepressure changes.
 6. The process according to claim 5, furthercomprising the steps of:continuously increasing the pressure from a lowpressure value to a maximum pressure value; when the pressure reachesthe maximum pressure value, generating the at least one compensatingsignal linearizing the pressure characteristic by the data processingsystem and providing the at least one compensating signal to theprogramming section; and continuously reducing the pressure from themaximum pressure value to the low pressure value while detecting the atleast one output pressure value and the at least one measurand value atthe predetermined frequency; and evaluating the at least one measurandvalue in the data processing system to determine a linearization result.